Beam switching method and related device

ABSTRACT

Embodiments provide a beam switching method and a related device. Under the method a first subframe sent by a base station by using a first beam can be received by a terminal device. The first subframe includes first-order downlink control information and second-order downlink control information. The terminal device can search for the second-order downlink control information based on the first-order downlink control information. The first-order downlink control information includes location indication information of the second-order downlink control information in the first subframe. The terminal device can switch from the first beam to a second beam based on the found second-order downlink control information to receive a second subframe. The downlink control information includes a switching indication field of the second beam. In this way, flexibility of beam switching is improved, load balancing of a control channel is implemented, and a latency of beam switching is reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/522,656, filed on Jul. 26, 2019, which is a continuation ofInternational Application No. PCT/CN2017/118134, filed on Dec. 23, 2017,which claims priority to Chinese Patent Application No. 201710057296.4,filed on Jan. 26, 2017. All of the afore-mentioned patent applicationsare hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to the field of wireless communications,and in particular, to a beam switching method and a related device.

BACKGROUND

In a beamforming (Beam Forming, BF) technology, a higher antenna arraygain can be implemented by spatially facing a specific direction. In a5th generation (5th-Generation, 5G) mobile communications technology,use of the beamforming technology for transmission is a key developmentdirection. For example, a key research direction in high frequency (HighFrequency, HF) communication is analog plus digital hybrid beamforming(Hybrid Beam Forming, HBF), so that not only a loss of a high frequencysignal due to a transmission distance is reduced, but also complexityand hardware costs are controlled within an acceptable range.

Analog beamforming may be implemented by using a phase shifter, and aphase of a radio frequency (Radio frequency, RF) link is adjusted byusing the phase shifter, so as to control a change in a direction of ananalog beam. The analog beamforming has a characteristic that analogbeams emitted from a same RF link can face only one direction at a sametime. In an analog beam-based transmission environment, a scenario inwhich an analog beam used for communication between a base station and aterminal device (User Equipment, UE) changes may occur, and therefore,the analog beam needs to be switched, so that communication can adapt tothe change of the analog beam.

In a solution 1 of the prior art, downlink control information (Downlinkcontrol information, DCI) may be used to indicate beam switching. Thereis a channel state information (Channel State Information, CSI)/beamstate information (Beam State Information, BSI)/beam refinementinformation (Beam Refinement Information, BRI) request (request) fieldin the DCI, and a length of the field is three bits. When a value of thefield is “001”, the base station instructs the UE to report BSI; or whena value of the field is “010”, the UE needs to measure a beam refinementreference signal (Beam Refinement Reference Signal, BRRS) and reportBRI. In addition, there is a 1-bit field in the DCI, and the field is abeam switch indication (Beam switch indication) used to instruct the UEto switch a beam.

For example, if CSI/BSI/BRI request=001 (or 010) and Beam switchindication=1 in the DCI received by the UE, the UE needs to switch thebeam, and the UE switches the beam at the beginning of an(n+kbeam-switch-delay-dic)^(th) subframe. Because beams for reportingthe BSI by the UE are in descending order of signal strength, the UEselects a first beam that is for reporting the BSI and with a strongestsignal to switch the beam, where n is a subframe in which the UE reportsthe BSI, and kbeam-switch-delay-dic=11. It is assumed that the UEreceives the DCI in a subframe n. In this case, the subframe in whichthe UE reports the BSI is n+4+m+1, where both m and l are notified byusing other fields in the DCI, m is a transmission time offset(transmission time offset) of a channel state information-referencesignal (Channel state information-reference signal, CSI-RS)/BRRS indownlink data, values of m are {0, 1, 2, and 3}, 1 is a transmissiontime offset of uplink data, values of 1 are {0, 1, . . . , and 7}, and asending period of the BRS may be (<5 ms, =5 ms, 10 ms, or 20 ms).

In a solution 2 of the prior art, a media access control-control element(Media Access Control-Control Element, MAC-CE) is used to indicate beamswitching. The base station sends the MAC CE to the UE, and the MAC CEincludes a 3-bit BRRS-RI and a 2-bit BR process index. The BRRS-RI isused to indicate a beam number, and the BR process index is used toindicate a BRRS process number. Four BR processes may be defined, amaximum of eight BRRS resources may be used in each BR process, and amaximum of eight antenna ports may be used for each BRRS resource.

For example, after the UE receives the MAC CE, the UE needs to switch abeam and adjust a serving beam to an indicated beam, and the UE switchesthe beam at the beginning of an (n+kbeamswitch-delay-mac)^(th) subframe,where n is a time when the UE feeds back a hybrid automatic repeatrequest (Hybrid auto repeat request, HARQ) positive acknowledgement(Acknowledgement, ACK), and kbeamswitch-delay-mac=14. It is assumed thatthe UE receives the MAC-CE in a subframe n. In this case, a subframe inwhich uplink control information (including the HARQ ACK) is reported isn+4+k+m, where both m and l are notified by using other fields in theDCI, m is a transmission time offset of a CSI-RS/BRRS in downlink data,values of m are {0, 1, 2, and 3}, l is a transmission time offset ofuplink data, values of 1 are {0, 1, . . . , and 7}, and one, two, five,or 10 OFDM symbols may be occupied for transmitting one BRRS.

However, when beam switching is controlled by using the DCI, the UE isalways instructed to switch to the first beam with a strongest signal.However, there is actually another available beam, and consequentlyflexibility of scheduling the beam switching is poor. A control latencyof the MAC-CE is longer than a control latency of the DCI, and when thebeam switching is controlled by using the MAC-CE, there is a problemthat a latency is relatively long.

SUMMARY

Technical problems to be resolved in embodiments of the presentinvention are that flexibility of scheduling beam switching is poor anda beam control time is long, and a beam switching method and a relateddevice are provided.

According to one aspect, an embodiment of the present invention providesa beam switching method, including:

first receiving, by a terminal device, a first subframe sent by a basestation by using a first beam, where the first subframe includesfirst-order downlink control information and second-order downlinkcontrol information; then searching for the second-order downlinkcontrol information based on the first-order downlink controlinformation, where the first-order downlink control information includeslocation indication information of the second-order downlink controlinformation in the first subframe; and finally, switching from the firstbeam to a second beam based on the found second-order downlink controlinformation to receive a second subframe, where the second downlinkcontrol information includes a switching indication field of the secondbeam. Therefore, flexibility of beam switching is improved, loadbalancing of a control channel is implemented by using the two-order DCIto transfer load on the control channel to a data channel, and incomparison with using a MAC CE to indicate beam switching, using DCI toindicate beam switching reduces a latency of beam switching.

In a possible design, a time-frequency resource location of thesecond-order DCI may be determined based on a configuration field in thefirst-order DCI, then a length of the second-order DCI is determinedbased on a length field in the first-order DCI, and information aboutthe length is decoded to obtain information about the second-order DCI.

In another possible design, a time interval between the first subframeand the second subframe is N subframes, and N is an integer greater thanor equal to 0. Alternatively, a time interval between the first subframeand the second subframe is M milliseconds/microseconds.

In another possible design, N or M may be a fixed value or a semi-staticvalue, and before the terminal device receives the first subframe sentby the base station by using the first beam, the terminal device mayreceive N or M notified by the base station by using a broadcastchannel, a master system information block, or a system informationblock, or through radio resource control.

In another possible design, N may alternatively be a dynamicallychanging value, and the second-order downlink control informationfurther includes indication information of N.

According to another aspect, an embodiment of the present inventionprovides a beam switching method, including:

first receiving, by a terminal device, a first subframe and a secondsubframe that are sent by a base station by using a first narrow beamwithin coverage of a first wide beam; and then switching from the firstnarrow beam within the coverage of the first wide beam to a secondnarrow beam within coverage of a second wide beam based on accesscontrol information in the first subframe and downlink controlinformation in the second subframe to receive a third subframe, wherethe access control information includes switching configurationinformation of the second wide beam, and the downlink controlinformation includes a switching indication field of the second narrowbeam. Beam switching accuracy is improved in a manner of jointindication of beam switching.

In a possible implementation, the terminal device first searches, basedon first-order downlink control information in the first subframe, forthe access control information that is in a data channel and that isindicated by second-order downlink control information in the firstsubframe, and searches for second-order downlink control information inthe second subframe based on first-order downlink control information inthe second subframe, where the first-order downlink control informationin the first subframe includes location indication information of thesecond-order downlink control information in the first subframe, and thefirst-order downlink control information in the second subframe includeslocation indication information of the second-order downlink controlinformation in the second subframe.

In another possible implementation, the terminal device switches fromthe first narrow beam within the coverage of the first wide beam to thesecond narrow beam within the coverage of the second wide beam based onthe found access control information that is in the data channel andthat is indicated by the second-order downlink control information inthe first subframe, and the found second-order downlink controlinformation in the second subframe.

In another possible implementation, the terminal device may search forthe second narrow beam within the coverage of the second wide beam froma preset beam mapping table based on the switching configurationinformation and the location indication information.

In another possible implementation, before the terminal device receivesthe first subframe and the second subframe that are sent by the basestation, the terminal device may receive the beam mapping table sent bythe base station by using a broadcast channel, or through radio resourcecontrol, or the like.

In another possible implementation, the terminal device may firstdetermine a time-frequency resource location of the second-order DCI inthe first subframe based on a configuration field in the first-order DCIin the first subframe, determine a length of the second-order DCI in thefirst subframe based on a length field in the first-order DCI in thefirst subframe, and decode information about the length to obtaininformation about the second-order DCI in the first subframe.

In another possible implementation, the terminal device may determine atime-frequency resource location of the second-order DCI in the secondsubframe based on a configuration field in the first-order DCI in thesecond subframe, determine a length of the second-order DCI in thesecond subframe based on a length field in the first-order DCI in thesecond subframe, and decode information about the length to obtaininformation about the second-order DCI in the second subframe.

In another possible implementation, a time interval between the firstsubframe and the third subframe is M subframes, a time interval betweenthe second subframe and the third subframe is N subframes, and M and Nare integers greater than or equal to 0.

In another possible implementation, N is a fixed value or a semi-staticvalue, M is a fixed value or a semi-static value, and before theterminal device receives the first subframe sent by the base station byusing the first beam, the terminal device may receive N and/or Mnotified by the base station by using a broadcast channel, a mastersystem information block, or a system information block, or throughradio resource control.

In another possible implementation, N is a dynamically changing value,and the second-order downlink control information in the first subframefurther includes indication information of M; and/or N is a dynamicallychanging value, and the second-order downlink control information in thethird subframe further includes indication information of N.

According to another aspect, an embodiment of the present inventionprovides a beam switching method, including:

first receiving, by a terminal device, a first subframe sent by a basestation by using a first beam, where the first subframe includesdownlink control information; and then switching from the first beam toa second beam based on the downlink control information to receive asecond subframe, where the downlink control information includes aswitching indication field of the second beam, the switching indicationfield includes a beam number, and the beam number is a quantity of bitsof a preset length, so that a latency of beam switching is reduced byusing DCI to indicate beam switching.

In a possible design, a beam number indicating beam switching is newlyadded to second-order DCI, and the beam number may be a quantity of bitsof a preset length.

In another possible implementation, N may be a fixed value or asemi-static value, and before the terminal device receives the firstsubframe sent by the base station by using the first beam, the terminaldevice may receive N notified by the base station by using a broadcastchannel, a master system information block, or a system informationblock, or through radio resource control.

In another possible implementation, N may alternatively be a dynamicallychanging value, and the second-order downlink control informationfurther includes indication information of N.

According to another aspect, an embodiment of the present inventionprovides a beam switching method, including:

sending, by a base station, a first subframe to a terminal device byusing a first beam, where the first subframe includes first-orderdownlink control information and second-order downlink controlinformation, the first-order downlink control information includeslocation indication information of the second-order downlink controlinformation in the first subframe, and the second downlink controlinformation includes a switching indication field of a second beam; andafter receiving the first subframe, switching, by the terminal device,from the first beam to the second beam to receive a second subframe, sothat flexibility of beam switching is improved, load balancing of acontrol channel is implemented by using the two-order DCI to transferload on the control channel to a data channel, and in comparison withusing a MAC CE to indicate beam switching, using DCI to indicate beamswitching reduces a latency of beam switching.

In a possible implementation, the switching indication field includes abeam number, and the beam number is a quantity of bits of a presetlength.

In another possible implementation, a time interval between the firstsubframe and the second subframe is N subframes, and N is an integergreater than or equal to 0.

In another possible implementation, N is a fixed value or a semi-staticvalue, and before the base station sends the first subframe to theterminal device by using the first beam, the base station sends N to theterminal device by using a broadcast channel, a master systeminformation block, or a system information block, or through radioresource control.

In another possible implementation, N is a dynamically changing value,and the second-order downlink control information further includesindication information of N.

According to another aspect, an embodiment of the present inventionprovides a beam switching method, including:

sending, by a base station, a first subframe and a second subframe to aterminal device by using a first narrow beam within coverage of a firstwide beam; and after receiving the first subframe and the secondsubframe, switching, by the terminal device, from the first narrow beamwithin the coverage of the first wide beam to a second narrow beamwithin coverage of a second wide beam based on access controlinformation in the first subframe and downlink control information inthe second subframe to receive a third subframe, where the accesscontrol information includes switching configuration information of thesecond wide beam, and the downlink control information includes aswitching indication field of the second narrow beam. Beam switchingaccuracy is improved in a manner of joint indication of beam switching.

In a possible implementation, before the base station sends the firstsubframe and the second subframe to the terminal device by using thefirst narrow beam within the coverage of the first wide beam, the basestation sends a preset beam mapping table to the terminal device byusing a broadcast channel.

In another possible implementation, the switching indication fieldincludes a beam number, the beam number is a quantity of bits of a firstpreset length, the access control information includes a beam groupnumber, and the beam group number is a quantity of bits of a secondpreset length.

In another possible implementation, a time interval between the firstsubframe and the third subframe is M subframes, a time interval betweenthe second subframe and the third subframe is N subframes, and M and Nare integers greater than or equal to 0.

In another possible implementation, before the base station sends thefirst subframe and the second subframe to the terminal device by usingthe first narrow beam within the coverage of the first wide beam, thebase station sends N and/or M to the terminal device by using abroadcast channel, a master system information block, or a systeminformation block, or through radio resource control.

In another possible implementation, N is a dynamically changing value,and second-order downlink control information in the first subframefurther includes indication information of M; and/or N is a dynamicallychanging value, and second-order downlink control information in thethird subframe further includes indication information of N.

According to another aspect, an embodiment of the present inventionprovides a beam switching method, including:

first sending, by a base station, a first subframe to a terminal deviceby using a first beam, where the first subframe includes downlinkcontrol information; and after receiving the first subframe, switching,by the terminal device, from the first beam to a second beam based onthe downlink control information to receive a second subframe, where thedownlink control information includes a switching indication field ofthe second beam, so that a latency of beam switching is reduced by usingthe DCI to indicate beam switching.

In another possible implementation, the switching indication fieldincludes a beam number, and the beam number is a quantity of bits of apreset length.

In another possible implementation, a time interval between the firstsubframe and the second subframe is N subframes, and N is an integergreater than or equal to 0.

In another possible implementation, N is a fixed value or a semi-staticvalue, and before the terminal device receives the first subframe sentby the base station by using the first beam, the base station sends N tothe terminal device by using a broadcast channel, a master systeminformation block, or a system information block, or through radioresource control.

In another possible implementation, N is a dynamically changing value,and second-order downlink control information further includesindication information of N.

According to another aspect, this application provides a terminaldevice, and the terminal device is configured to implement the methodand the function that are performed by the foregoing terminal device,and is implemented by hardware/software, where the hardware/softwareincludes a unit corresponding to the function.

According to another aspect, this application provides a base station,and the base station is configured to implement the method and thefunction that are performed by the foregoing base station, and isimplemented by hardware/software, where the hardware/software includes aunit corresponding to the function.

According to another aspect, this application provides a beam switchingdevice, including a processor, a memory, and a communications bus. Thecommunications bus is configured to implement connection andcommunication between the processor and the memory, and the processorexecutes a program stored in the memory, to implement the steps in thebeam switching method provided above.

According to another aspect, this application provides a beam switchingdevice, including a processor, a memory, and a communications bus. Thecommunications bus is configured to implement connection andcommunication between the processor and the memory, and the processorexecutes a program stored in the memory, to implement the steps in thebeam switching method provided above.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention or in the background more clearly, the following describes theaccompanying drawings required for describing the embodiments of thepresent invention or the background.

FIG. 1 is a schematic structural diagram of a beam switching systemaccording to an embodiment of the present invention;

FIG. 2 is a schematic flowchart of a beam switching method according toan embodiment of the present invention;

FIG. 3(A) is a schematic structural diagram of locations of one type oftwo-order DCI according to an embodiment of the present invention;

FIG. 3(B) is a schematic structural diagram of locations of another typeof two-order DCI according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of DCI configuration information accordingto an embodiment of the present invention;

FIG. 5 is a schematic diagram of one type of beam switching according toan embodiment of the present invention;

FIG. 6 is a schematic flowchart of another beam switching methodaccording to an embodiment of the present invention;

FIG. 7 is a schematic diagram of beam coverage according to anembodiment of the present invention;

FIG. 8 is a schematic diagram of a beam mapping table according to anembodiment of the present invention;

FIG. 9 is a schematic diagram of another type of beam switchingaccording to an embodiment of the present invention;

FIG. 10 is a schematic flowchart of still another beam switching methodaccording to an embodiment of the present invention;

FIG. 11 is a schematic diagram of still another type of beam switchingaccording to an embodiment of the present invention;

FIG. 12 is a schematic structural diagram of a terminal device accordingto an embodiment of the present invention;

FIG. 13 is a schematic structural diagram of a base station according toan embodiment of the present invention;

FIG. 14 is a schematic structural diagram of a beam switching deviceaccording to an embodiment of the present invention; and

FIG. 15 is a schematic structural diagram of another beam switchingdevice according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

The following describes the embodiments of the present invention withreference to the accompanying drawings in the embodiments of the presentinvention.

The terms “first” and “second” in the embodiments of the presentinvention are merely intended for a purpose of description, and shallnot be understood as an indication or implication of relative importanceor implicit indication of a quantity of indicated technical features.Therefore, a feature restricted by “first” or “second” may explicitly orimplicitly include one or more features.

FIG. 1 is a schematic structural diagram of a beam switching systemaccording to an embodiment of the present invention. The beam switchingsystem includes a base station and a terminal device. A plurality ofavailable analog beams are maintained between the base station and theterminal device for communication. In addition, the base station may usesingle-order DCI or two-order DCI to instruct UE to switch a beam. Thesingle-order DCI or the two-order DCI exists independently, and whenaccessing a network, the UE already knows a type of DCI used in thecurrent network.

The terminal device in this embodiment of the present invention may bereferred to as an access terminal, a subscriber unit, a subscriberstation, a mobile station, a mobile console, a remote station, a remoteterminal, a mobile device, a user terminal, a terminal, a wirelesscommunications device, a user agent, or a user apparatus. The accessterminal may be a cellular phone, a cordless phone, a session initiationprotocol (Session Initiation Protocol, SIP) phone, a wireless local loop(Wireless Local Loop, WLL) station, a personal digital assistant(Personal Digital Assistant, PDA), a handheld device having a wirelesscommunication function, a computing device, another processing deviceconnected to a wireless modem, an in-vehicle device, a wearable device,a terminal device in a future 5G network, or the like.

The base station in this embodiment of the present invention may be abase transceiver station (Base Transceiver Station, BTS) in a globalsystem for mobile communications (Global System for MobileCommunication, GSM) system or a code division multiple access (CodeDivision Multiple Access, CDMA) system, or may be a NodeB (NodeB, NB) ina WCDMA system, or may be an evolved NodeB (Evolutional Node B, ENB) inan LTE system. Alternatively, the base station may be a relay node, anaccess point, an in-vehicle device, or a wearable device, or may be awireless fidelity (Wireless-Fidelity, Wi-Fi) station, or may be a basestation in next-generation communication, such as a 5G radio accessnetwork device (New Radio, NR, or referred to as a “new radiotechnology”, a base station, a small cell, or a micro cell).

FIG. 2 is a schematic flowchart of a beam switching method according toan embodiment of the present invention. In this embodiment of thepresent invention, two-order DCI is used to indicate beam switching. Themethod includes but is not limited to the following steps.

S201. A terminal device receives a first subframe sent by a base stationby using a first beam, where the first subframe includes first-orderdownlink control information and second-order downlink controlinformation.

In one implementation, a plurality of available analog beams aremaintained between the base station and the terminal device. Forexample, the base station and the terminal device perform downlink datatransmission by using an analog beam 1. When the analog beam 1 is nolonger applicable because the terminal device moves, the base stationdetermines, based on a channel measurement result and a channelscheduling result, that the analog beam 1 serving the terminal deviceneeds to be switched. Therefore, to instruct the terminal device in atimely manner to perform beam switching, the base station may send thefirst subframe to the terminal device by using the first beam.

In this embodiment of the present invention, the two-order DCI is usedto instruct the terminal device to perform the beam switching. Thefirst-order DCI is sent on a physical downlink control channel (Physicaldownlink control channel, PDCCH), and the second-order DCI may be sentat a resource location of the PDCCH or at a resource location of aphysical downlink data channel (Physical downlink shared channel,PDSCH). As shown in FIG. 3(A) and FIG. 3(B), the first-order DCI islocated at a beginning location of a subframe, and may be located at asame location as single-order DCI of LTE, and the second-order DCI maybe located at a resource location on a control channel (such assecond-order DCI of UE 2 in FIG. 3(A)) or at a resource location on adata channel (such as second-order DCI of UE 1 in FIG. 3(B)). Thefirst-order DCI has a fixed size, may include at least indications of alocation and a size of the second-order DCI, and may further includesome data decoding information. The second-order DCI has a variable sizeand may include other required control information.

It should be noted that because there are many defined DCI formats, theUE needs to attempt to decode DCI according to a length of the DCI. Thetwo-order DCI is used, the first-order DCI has a fixed length, and thesecond-order DCI does not require blind detection because thesecond-order DCI is already indicated in the first-order DCI. Complexityof the blind detection is reduced in comparison with the single-orderDCI. In addition, the second-order DCI may be transmitted at theresource location on the data channel. In this way, a resource of thecontrol channel is saved and may be used to control more UEs. Therefore,the two-order DCI actually transfers load of the control channel to thedata channel, thereby maintaining load balancing of resources of thecontrol channel.

S202. The terminal device searches for the second-order downlink controlinformation based on the first-order downlink control information, wherethe first-order downlink control information includes locationindication information of the second-order downlink control informationin the first subframe.

In one implementation, a time-frequency resource location of thesecond-order DCI may be determined based on a configuration field in thefirst-order DCI, then a length of the second-order DCI is determinedbased on a length field in the first-order DCI, and information aboutthe length is decoded to obtain information about the second-order DCI.

As shown in FIG. 4, a “second-order DCI resource configuration method”and a “second-order DCI length” are predefined in the first-order DCI.The terminal device may find, in the “second-order DCI resourceconfiguration method” in the first-order DCI, a resource block used totransmit the second-order DCI, and then determine the length of thesecond-order DCI in the “second-order DCI length” in the first-orderDCI, so as to decode the information about the length to obtain theinformation about the second-order DCI.

S203. The terminal device switches from the first beam to a second beambased on the found second-order downlink control information to receivea second subframe, where the second downlink control informationincludes a switching indication field of the second beam.

In one implementation, the second-order DCI includes a switchingindication field, and the switching indication field instructs theterminal device to switch to a beam X. The beam X may be a beam withstrongest signal strength, or may be a beam with weakest signalstrength, or may be a beam with other signal strength. The base stationmay select a beam with different signal strength each time to instructthe terminal device to perform beam switching. A beam number indicatingbeam switching is newly added to the second-order DCI, and the beamnumber may be a quantity of bits of a preset length. For example, thereare a total of N=8 analog beams {0, 1, . . . , and 7} in a system, andin this case, a length of the switching indication field is three bits.When a second-order DCI field decoded by the UE is “010”, the terminaldevice switches to a third analog beam; or if a second-order DCI fielddecoded by the UE is “111”, the terminal device switches to an eighthanalog beam.

A time interval between the first subframe and the second subframe is Nsubframes, and N is an integer greater than or equal to 0.Alternatively, a time interval between the first subframe and the secondsubframe is M milliseconds/microseconds, and M is a number greater thanor equal to 0. N or M may be a fixed value or a semi-static value, andbefore the terminal device receives the first subframe sent by the basestation by using the first beam, the terminal device may receive N or Mnotified by the base station by using a broadcast channel, a mastersystem information block, or a system information block, or throughradio resource control.

In some embodiments, N may alternatively be a dynamically changingvalue, and the second-order downlink control information furtherincludes indication information of N. Another field may be added to thesecond-order DCI. The field is used to identify a switching timesequence and dynamically notify the UE of a time of switching a beam. Tobe specific, if the UE receives a beam switch indication in an n^(th)subframe, the UE starts switching the beam in an (n+k)^(th) subframe,for example, k={0, 1, . . . , and 7}, and if the UE obtains throughdecoding that the field is “111”, the UE starts switching the beam in an(n+7)^(th) subframe.

In conclusion, FIG. 5 is a schematic diagram of one type of beamswitching according to an embodiment of the present invention. In ann^(th) subframe, a base station and UE perform communication by using ananalog beam 1. The terminal device first finds second-order DCI based onfirst-order DCI, and then switches from the analog beam 1 to an analogbeam 2 based on a switching indication field in the second-order DCI, sothat the base station and the UE perform communication by using theanalog beam 2 in an (n+k)^(th) subframe. Therefore, flexibility of beamswitching is improved, load balancing of a control channel isimplemented by using the two-order DCI to transfer load on the controlchannel to a data channel, and in comparison with using a MAC CE toindicate beam switching, using DCI to indicate beam switching reduces alatency of beam switching.

FIG. 6 is a schematic flowchart of a beam switching method according toan embodiment of the present invention. Because a wide beam hasrelatively large coverage, the wide beam that can cover UE changesrelatively slowly. Because a narrow beam has relatively small coverage,the narrow beam that can serve UE may change relatively fast. Therefore,a manner of joint indication of beam switching is used in thisembodiment of the present invention, and includes the following steps.

S601. A terminal device receives a first subframe and a second subframethat are sent by a base station.

In one implementation, a plurality of available analog beams aremaintained between the base station and the terminal device. Forexample, when an analog beam 1 is no longer applicable because theterminal device moves, the base station determines, based on a channelmeasurement result and a channel scheduling result, that the analog beam1 serving the terminal device needs to be switched. Therefore, toinstruct the terminal device in a timely manner to perform beamswitching and reduce resource overheads, the base station may first sendthe first subframe and the second subframe to the terminal device byusing a first narrow beam within coverage of a first wide beam.

It should be noted that if an analog beam is relatively narrow in asystem, a total quantity N of analog beams is relatively large, aquantity of bits of a beam number is relatively large, and relativelyhigh overheads are caused. Therefore, narrow beams may be grouped.Narrow beams that can cover a continuous space range may be grouped as awide beam (also referred to as a beam group), or narrow beams that covera discontinuous space range may be grouped as a wide beam (also referredto as a beam group). The wide beam may be a physical concept that reallyexists, that is, a beam that can really be used in the system; or may bea logical concept, that is, there is no real physical wide beam in thesystem, but a logical representation of a group of narrow beams. FIG. 7is a schematic diagram of beam coverage according to an embodiment ofthe present invention. There may be 32 narrow beams and eight wide beamsin a cell served by a base station (only one wide beam and four narrowbeams covered by the wide beam are depicted in the figure), and coverageof each wide beam may be a set of coverage of more than four narrowbeams.

S602. The terminal device switches from a first narrow beam withincoverage of a first wide beam to a second narrow beam within coverage ofa second wide beam based on access control information in the firstsubframe and downlink control information in the second subframe toreceive a third subframe, where the access control information includesswitching configuration information of the second wide beam, and thedownlink control information includes a switching indication field ofthe second narrow beam. The switching indication field includes a beamnumber, the beam number is a quantity of bits of a first preset length,the access control information includes a beam group number, and thebeam group number is a quantity of bits of a second preset length. Theaccess control information may be MAC CE information.

In one implementation, the terminal device first searches, based on thefirst-order downlink control information in the first subframe, for theaccess control information that is in a data channel and that isindicated by the second-order downlink control information in the firstsubframe, and searches for the second-order downlink control informationin the second subframe based on the first-order downlink controlinformation in the second subframe, where the first-order downlinkcontrol information in the first subframe includes location indicationinformation of the second-order downlink control information in thefirst subframe, and the first-order downlink control information in thesecond subframe includes location indication information of thesecond-order downlink control information in the second subframe. Then,the terminal device switches from the first narrow beam within thecoverage of the first wide beam to the second narrow beam within thecoverage of the second wide beam based on the found access controlinformation that is in the data channel and that is indicated by thesecond-order downlink control information in the first subframe, and thefound second-order downlink control information in the second subframe.Specifically, the second narrow beam within the coverage of the secondwide beam may be searched for from a preset beam mapping table based onthe switching configuration information and the location indicationinformation.

In some embodiments, before the terminal device receives the firstsubframe and the second subframe that are sent by the base station, theterminal device may receive the beam mapping table sent by the basestation by using a broadcast channel, or through radio resource control,or the like. The base station may send the beam mapping table to theterminal device when the terminal device accesses a network, so that thebeam mapping table is visible to both the base station and the terminaldevice.

Further, the terminal device may first determine a time-frequencyresource location of the second-order DCI in the first subframe based ona configuration field in the first-order DCI in the first subframe,determine a length of the second-order DCI in the first subframe basedon a length field in the first-order DCI in the first subframe, anddecode information about the length to obtain information about thesecond-order DCI in the first subframe. Then, the terminal devicedetermines information such as a time-frequency resource location, atransmission mode, or a modulation and coding scheme of data in thefirst subframe based on a configuration field in the second-order DCI inthe first subframe, obtains data information in the first subframethrough decoding, and obtains a MAC-CE from the data information.

As shown in FIG. 4, a “second-order DCI resource configuration method”and a “second-order DCI length” are predefined in the first-order DCI.The terminal device may find, in the “second-order DCI resourceconfiguration method” in the first-order DCI, a resource block used totransmit the second-order DCI, and then determine the length of thesecond-order DCI in the “second-order DCI length” in the first-orderDCI, so as to decode the information about the length to obtain theinformation about the second-order DCI. “Control information related todownlink data scheduling” and “control information related tomulti-antenna transmission” are defined in the second-order DCI, and theterminal device may obtain, at the time-frequency resource locationindicated by the second-order DCI, data information through decoding byusing information such as a transmission mode and a modulation andcoding scheme indicated by the second-order DCI, and obtain MAC-CEinformation from the data information. The MAC-CE information includesthe switching configuration information of the second wide beam, and theswitching configuration information instructs the terminal device toswitch to a wide beam of a beam group numbered X.

In some embodiments, after the UE receives, in an n^(th) subframe,MAC-CE information that is sent by the base station and that indicatesswitching to a wide beam, the UE performs the switching to the wide beamin an (n+k2)^(th) subframe, and selects a narrow beam within coverage ofthe wide beam to perform switching. For example, during the switching tothe wide beam, a number of the wide beam is selected based on the MAC-CEinformation, and a logical number of the narrow beam remains unchanged.Alternatively, a number of the wide beam is selected based on the MAC-CEinformation, and a narrow beam with a logical number 0 is selected.However, specific implementation is not limited to the foregoing twomanners.

It should be noted that DCI is control information at a physical layer(layer 1), and a MAC-CE is control information at a MAC layer (layer 2).The MAC-CE is actually a bit sequence, a plurality of fields are definedin the MAC-CE, and each field is used to control a specific function.MAC-CE information is transmitted on the data channel, and therefore,the MAC-CE information is carried in data. On a base station side, theMAC-CE is first encapsulated into data, and the data is sent on aspecific time-frequency resource in a form of an electromagnetic waveafter channel coding, amplitude modulation, and waveform modulation.After receiving the electromagnetic wave, the UE receives the datachannel at a specific time-frequency resource location, and obtains anoriginal bit sequence of the MAC-CE by performing a series of decodingprocesses such as demodulation, channel decoding, and decapsulationopposite to processes on the base station side. The UE performs acorresponding operation according to an instruction of each field and arequirement of the base station. Unlike the DCI, the MAC-CE needs to beencapsulated into data of the layer 1 when the MAC-CE is to be sent, andwhen the data is to be received, the data needs to be first received atthe layer 1 and then decapsulated and interpreted at the layer 2.Therefore, a control latency of the MAC-CE is longer than a controllatency of the DCI.

Further, the terminal device may determine a time-frequency resourcelocation of the second-order DCI in the second subframe based on aconfiguration field in the first-order DCI in the second subframe,determine a length of the second-order DCI in the second subframe basedon a length field in the first-order DCI in the second subframe, anddecode information about the length to obtain information about thesecond-order DCI in the second subframe. The second-order DCI in thesecond subframe includes a switching indication field, and the switchingindication field instructs the terminal device to switch to a narrowbeam with a logical number Y.

As shown in FIG. 4, a “second-order DCI resource configuration method”and a “second-order DCI length” are predefined in the first-order DCI.The terminal device may find, in the “second-order DCI resourceconfiguration method” in the first-order DCI, a resource block used totransmit the second-order DCI, and then determine the length of thesecond-order DCI in the “second-order DCI length” in the first-orderDCI, so as to decode the information about the length to obtain theinformation about the second-order DCI. Indication information forcontrolling beam switching is newly added to the second-order DCI, andthe indication information may include a beam number indication. Forexample, there are a total of N=8 analog narrow beams {0, 1, . . . , and7} in a system, and in this case, a length of the switching indicationfield is three bits. When a second-order DCI field decoded by the UE is“010”, the terminal device switches to a third analog narrow beam; or ifa second-order DCI field decoded by the UE is “111”, the terminal deviceswitches to an eighth analog narrow beam.

For example, FIG. 8 is a schematic diagram of a correspondence that isbetween a beam number in a MAC-CE and a beam number in DCI and that ispre-agreed between the base station and the terminal device. If theMAC-CE indicates a beam group number 2, and the DCI indicates a logicalbeam number 0, the terminal device switches to a narrow beam 0 withincoverage of a wide beam 2, namely, a physical narrow beam 8. If theMAC-CE indicates a beam group number 7, and the DCI indicates a logicalbeam number 3, the terminal device switches to a narrow beam 7 withincoverage of a wide beam 3, namely, a physical narrow beam 31.

A time interval between the first subframe and the third subframe is Msubframes, a time interval between the second subframe and the thirdsubframe is N subframes, and M and N are integers greater than or equalto 0. N is a fixed value or a semi-static value, M is a fixed value or asemi-static value, and before the terminal device receives the firstsubframe sent by the base station by using the first beam, the terminaldevice may receive N and/or M notified by the base station by using abroadcast channel, a master system information block, or a systeminformation block, or through radio resource control.

In some embodiments, N is a dynamically changing value, and thesecond-order downlink control information in the first subframe furtherincludes indication information of M; and/or N is a dynamically changingvalue, and the second-order downlink control information in the thirdsubframe further includes indication information of N. Another field maybe added to the second-order DCI. The field is used to identify aswitching time sequence and dynamically notify the UE of a time ofswitching a beam. To be specific, if the UE receives a beam switchindication in an n^(th) subframe, the UE starts switching the beam in an(n+k)^(th) subframe, for example, k={0, 1, . . . , and 7}, and if the UEobtains through decoding that the field is “111”, the UE startsswitching the beam in an (n+7)^(th) subframe.

For a manner of joint indication of beam switching by using a mappingrelationship between a layer L1 and a layer L2, FIG. 9 is a schematicdiagram of one type of beam switching. In an n^(th) subframe, the basestation and the UE perform communication by using a narrow beam 2 in abeam group 0, MAC-CE information is found by using two-order DCI, and itis determined that the terminal device needs to switch to a beam group1. In an (n+k1)^(th) subframe, the base station and the UE performcommunication also by using the narrow beam 2 in the beam group 0,second-order DCI is found by using first-order DCI, and it is determinedthat the terminal device needs to switch to a narrow beam 7. Finally, byjointly using two types of indication information, the terminal deviceswitches from the narrow beam 2 in the beam group 0 to the narrow beam 7in the beam group 1, and in an (n+k2)^(th) subframe, the base stationand the UE perform communication by using the narrow beam 7 in the beamgroup 1. In particular, in a time relationship, k1=k2−k, where k1 is alength of a time from receiving, by the UE, a MAC-CE configuration thatrequires beam switching to receiving DCI that indicates the beamswitching, k is a length of a time from receiving, by the UE, the DCIthat indicates the beam switching to switching a beam, k2 is a length ofa time from receiving, by the UE, the MAC-CE configuration that requiresthe beam switching to switching the beam, and usually, k is less thank2.

It should be noted that the first subframe and the second subframe arenot limited in an order of a receiving time. The first subframe may befirst received, wide beam switching is indicated based on the accesscontrol information in the first subframe, then the second subframe isreceived, and narrow beam switching is indicated based on the DCIinformation in the second subframe, thereby completing the jointindication of the beam switching. Alternatively, the second subframe maybe first received, narrow beam switching is indicated based on the DCIinformation in the second subframe, then the first subframe is received,and wide beam switching is indicated based on the access controlinformation in the first subframe, thereby completing the jointindication of the beam switching.

In this embodiment of the present invention, the access controlinformation is not limited to the MAC CE information at the layer L2,but may further include an RRC IE at a layer L3. A specificimplementation of a manner in which beam switching is jointly indicatedby using the DCI and the RRC IE is similar to a manner in which the beamswitching is jointly indicated by using the DCI and the MAC CE. Detailsare not described in this embodiment of the present invention again.

FIG. 10 is a schematic flowchart of a beam switching method according toan embodiment of the present invention. In this embodiment of thepresent invention, single-order DCI is used to indicate beam switching.The method includes but is not limited to the following steps.

S1001. A terminal device receives a first subframe sent by a basestation by using a first beam, where the first subframe includesdownlink control information.

In specific implementation, a plurality of available analog beams aremaintained between the base station and the terminal device. Forexample, the base station and the terminal device perform downlink datatransmission by using an analog beam 1. When the analog beam 1 is nolonger applicable because the terminal device moves, the base stationdetermines, based on a channel measurement result and a channelscheduling result, that the analog beam 1 serving the terminal deviceneeds to be switched. Therefore, to instruct the terminal device in atimely manner to perform beam switching, the base station may send thefirst subframe to the terminal device by using the first beam.

S1002. The terminal device switches from the first beam to a second beambased on the downlink control information to receive a second subframe,where the downlink control information includes a switching indicationfield of the second beam.

In one implementation, the DCI includes a switching indication field,and the switching indication field instructs the terminal device toswitch to a beam X. A beam number indicating beam switching is newlyadded to second-order DCI, and the beam number may be a quantity of bitsof a preset length. For example, there are a total of N=8 analog beams{0, 1, . . . , and 7} in a system, and in this case, a length of theswitching indication field is three bits. When a second-order DCI fielddecoded by the UE is “010”, the terminal device switches to a thirdanalog beam; or if a second-order DCI field decoded by the UE is “111”,the terminal device switches to an eighth analog beam.

In some embodiments, a time interval between the first subframe and thesecond subframe is N subframes, and N is an integer greater than orequal to 0. N may be a fixed value or a semi-static value, and beforethe terminal device receives the first subframe sent by the base stationby using the first beam, the terminal device may receive N notified bythe base station by using a broadcast channel, a master systeminformation block, or a system information block, or through radioresource control.

In some embodiments, N may alternatively be a dynamically changingvalue, and the second-order downlink control information furtherincludes indication information of N. Another field may be added to theDCI. The field is used to identify a switching time sequence anddynamically notify the UE of a time of switching a beam. To be specific,if the UE receives a beam switch indication in an n^(th) subframe, theUE starts switching the beam in an (n+k)^(th) subframe, for example,k={0, 1, . . . , and 7}, and if the UE obtains through decoding that thefield is “111”, the UE starts switching the beam in an (n+7)^(th)subframe.

In conclusion, FIG. 11 is a schematic diagram of one type of beamswitching according to an embodiment of the present invention. In ann^(th) subframe, a base station and UE perform communication by using ananalog beam 1. The terminal device first switches from the analog beam 1to an analog beam 2 based on a switching indication field in DCI, sothat the base station and the UE perform communication by using theanalog beam 2 in an (n+k)^(th) subframe, and a latency of beam switchingis reduced by using DCI to indicate beam switching.

FIG. 12 is a schematic structural diagram of a terminal device accordingto an embodiment of the present invention. As shown in the figure, theterminal device includes a receiving module 1201 and a processing module1202. The receiving module 1201 and the processing module 1202 performthe method and the function that are performed by the terminal device inthe foregoing embodiment, including: The receiving module 1201 isconfigured to receive a first subframe sent by a base station, and theprocessing module 1202 is configured to: search for second-orderdownlink control information based on first-order downlink controlinformation in the first subframe, and switch from a first beam to asecond beam based on the found second-order downlink controlinformation. Alternatively, the receiving module 1201 is configured toreceive a first subframe and a second subframe that are sent by a basestation, and the processing module 1202 is configured to switch from afirst narrow beam within coverage of a first wide beam to a secondnarrow beam within coverage of a second wide beam based on accesscontrol information in the first subframe and downlink controlinformation in the second subframe. Alternatively, the receiving module1201 is configured to receive a first subframe sent by a base station,and the processing module 1202 is configured to switch from a first beamto a second beam based on downlink control information to receive asecond subframe. A specific implementation is not described in thisembodiment of the present invention.

FIG. 13 is a schematic structural diagram of a base station according toan embodiment of the present invention. As shown in the figure, the basestation includes a sending module. The sending module performs themethod and the function that are performed by the base station in theforegoing embodiment. The sending module is specifically configured tosend, to a terminal device, a subframe that carries downlink controlinformation. A specific implementation is not described in thisembodiment of the present invention.

FIG. 14 is a schematic structural diagram of a beam switching deviceaccording to the present invention. As shown in the figure, the devicemay include: at least one processor 1401 such as a CPU, at least onenetwork interface 1402, at least one memory 1403, and at least onecommunications bus 1404. The communications bus 1404 is configured toimplement connection and communication between these components. Thenetwork interface 1402 of the device in this embodiment of the presentinvention is configured to perform signaling or data communication withanother node device. The memory 1403 may be a high-speed RAM memory, ormay be a non-volatile memory (non-volatile memory), such as at least onemagnetic disk memory. Optionally, the memory 1403 may be at least onestorage apparatus far away from the processor 1401. The memory 1403stores a group of program code, and the processor 1401 executes aprogram in the memory 1403 that is executed by the foregoing radioaccess network node.

Specifically, the processor is configured to invoke the program code toperform the following operations:

receiving, by using the network interface 1402, a first subframe sent bya base station by using a first beam, where the first subframe includesfirst-order downlink control information and second-order downlinkcontrol information;

searching for the second-order downlink control information based on thefirst-order downlink control information, where the first-order downlinkcontrol information includes location indication information of thesecond-order downlink control information in the first subframe; and

switching from the first beam to a second beam based on the foundsecond-order downlink control information to receive a second subframe,where the second downlink control information includes a switchingindication field of the second beam.

Alternatively, the processor is configured to invoke the program code toperform the following operations:

receiving, by using the network interface 1402, a first subframe and asecond subframe that are sent by a base station by using a first narrowbeam within coverage of a first wide beam; and

switching from the first narrow beam within the coverage of the firstwide beam to a second narrow beam within coverage of a second wide beambased on access control information in the first subframe and downlinkcontrol information in the second subframe to receive a third subframe,where the access control information includes switching configurationinformation of the second wide beam, and the downlink controlinformation includes a switching indication field of the second narrowbeam.

Alternatively, the processor is configured to invoke the program code toperform the following operations:

receiving, by using the network interface 1402, a first subframe sent bya base station by using a first beam, where the first subframe includesdownlink control information; and

switching from the first beam to a second beam based on the downlinkcontrol information to receive a second subframe, where the downlinkcontrol information includes a switching indication field of the secondbeam, the switching indication field includes a beam number, and thebeam number is a quantity of bits of a preset length.

Further, the processor may further cooperate with the memory and thenetwork interface to perform the operations of the terminal device inthe foregoing embodiment of the present invention.

FIG. 15 is a schematic structural diagram of a beam switching deviceaccording to the present invention. As shown in the figure, the devicemay include: at least one processor 1501 such as a CPU, at least onenetwork interface 1502, at least one memory 1503, and at least onecommunications bus 1504. The communications bus 1504 is configured toimplement connection and communication between these components. Thenetwork interface 1502 of the device in this embodiment of the presentinvention is configured to perform signaling or data communication withanother node device. The memory 1503 may be a high-speed RAM memory, ormay be a non-volatile memory (non-volatile memory), such as at least onemagnetic disk memory. In some embodiments, the memory 1503 may be atleast one storage apparatus far away from the processor 1501. The memory1503 stores a group of program code, and the processor 1501 executes aprogram in the memory 1503 that is executed by the foregoing radioaccess network node.

The processor 1501 configures first-order downlink control informationand second-order downlink control information in a first subframe, wherethe first-order downlink control information includes locationindication information of the second-order downlink control informationin the first subframe, and the second downlink control informationincludes a switching indication field of the second beam. Thecommunications bus 1504 sends the first subframe to a terminal device byusing a first beam.

Alternatively, the processor 1501 configures access control informationin a first subframe and downlink control information in a secondsubframe, where the access control information includes switchingconfiguration information of the second wide beam, and the downlinkcontrol information includes a switching indication field of the secondnarrow beam. The network interface 1502 sends the first subframe and thesecond subframe to a terminal device by using a first narrow beam withincoverage of a first wide beam.

Alternatively, the processor 1501 configures downlink controlinformation in a first subframe, the network interface 1502 sends thefirst subframe to a terminal device by using a first beam, and thedownlink control information is used by the terminal device to switchfrom the first beam to a second beam to receive a second subframe.

Further, the processor may further cooperate with the memory and thenetwork interface to perform the operations of the base station in theforegoing embodiment of the present invention.

A person of ordinary skill in the art may understand that all or some ofthe processes of the methods in the embodiments may be implemented by acomputer program instructing related hardware. The program may be storedin a computer readable storage medium. When the program runs, theprocesses in the method embodiments are performed. The storage mediumincludes: any medium that can store program code, such as a ROM, arandom access memory RAM, a magnetic disk, or an optical disc.

What is claimed is:
 1. A terminal device, wherein the terminal devicecomprises: a receiver, configured to receive a first subframe sent by abase station using a first beam, wherein the first subframe comprisesfirst-order downlink control information and second-order downlinkcontrol information; and a processor, configured to search for thesecond-order downlink control information based on the first-orderdownlink control information, wherein the first-order downlink controlinformation comprises location indication information of thesecond-order downlink control information in the first subframe, whereinthe processor is further configured to switch from the first beam to asecond beam based on the second-order downlink control information toreceive a second subframe, wherein the second downlink controlinformation comprises a switching indication field of the second beam.2. The terminal device according to claim 1, wherein the switchingindication field comprises a beam number, wherein the beam number is aquantity of bits of a preset length.
 3. The terminal device according toclaim 1, wherein a time interval between the first subframe and thesecond subframe is N subframes, wherein N is an integer greater than orequal to
 1. 4. The terminal device according to claim 3, wherein N is adynamically changing value, and the second-order downlink controlinformation further comprises indication information of N.
 5. A terminaldevice, wherein the terminal device comprises: a receiver, configured toreceive a first subframe and a second subframe sent by a base station;and a processor, configured to switch from a first narrow beam withincoverage of a first wide beam to a second narrow beam within coverage ofa second wide beam based on access control information in the firstsubframe and downlink control information in the second subframe toreceive a third subframe, wherein the access control informationcomprises switching configuration information of the second wide beam,and the downlink control information comprises a switching indicationfield of the second narrow beam.
 6. The terminal device according toclaim 5, wherein both the first subframe and the second subframecomprise first-order downlink control information and second-orderdownlink control information; and, wherein the processor is configuredto: search, based on the first-order downlink control information in thefirst subframe, for the access control information that is in a datachannel and that is indicated by the second-order downlink controlinformation in the first subframe, and search for the second-orderdownlink control information in the second subframe based on thefirst-order downlink control information in the second subframe, whereinthe first-order downlink control information in the first subframecomprises location indication information of the second-order downlinkcontrol information in the first subframe, and the first-order downlinkcontrol information in the second subframe comprises location indicationinformation of the second-order downlink control information in thesecond subframe; and switch from the first narrow beam within thecoverage of the first wide beam to the second narrow beam within thecoverage of the second wide beam based on the access controlinformation, and the second-order downlink control information.
 7. Theterminal device according to claim 6, wherein the processor isconfigured to: search for the second narrow beam within the coverage ofthe second wide beam from a preset beam mapping table based on theswitching configuration information and the location indicationinformation, wherein the beam mapping table is sent by the base station.8. The terminal device according to claim 5, wherein: the switchingindication field comprises a beam number, the beam number being aquantity of bits of a first preset length, and the access controlinformation comprises a beam group number, the beam group number being aquantity of bits of a second preset length.
 9. The terminal deviceaccording to claim 5, wherein a time interval between the first subframeand the third subframe is M subframes, a time interval between thesecond subframe and the third subframe is N subframes, wherein M and Nare integers greater than or equal to
 0. 10. The terminal deviceaccording to claim 9, wherein N is a dynamically changing value, and thesecond-order downlink control information in the first subframe furthercomprises indication information of M; and/or N is a dynamicallychanging value, and the second-order downlink control information in thethird subframe further comprises indication information of N.
 11. Aterminal device, wherein the terminal device comprises: a receiver,configured to receive a first subframe sent by a base station by using afirst beam, wherein the first subframe comprises downlink controlinformation; and a processor, configured to switch from the first beamto a second beam based on the downlink control information to receive asecond subframe, wherein the downlink control information comprises aswitching indication field of the second beam, the switching indicationfield comprising a beam number, the beam number being a quantity of bitsof a preset length.
 12. The terminal device according to claim 11,wherein the switching indication field comprises a beam number, whereinthe beam number is a quantity of bits of a preset length.
 13. Theterminal device according to claim 11, wherein a time interval betweenthe first subframe and the second subframe is N subframes, wherein N isan integer greater than or equal to
 0. 14. The terminal device accordingto claim 13, wherein N is a dynamically changing value, and thesecond-order downlink control information further comprises indicationinformation of N.